The present invention relates to novel aqueous copolymer dispersions, to processes for preparing them and to their use in particular in elastic coatings.
EP-A-0 458 144 discloses aqueous synthetic resin dispersions whose synthetic resins contain in copolymerized form not only monomers such as acrylic or methacrylic esters, styrene and vinyl esters, monoethylenically unsaturated acetophenone derivatives and/or benzophenone derivatives but also at least one unsaturated ketone or one aldehyde, and also comprise a compound containing at least two acid hydrazide groups, and are obtained by free-radical emulsion polymerization. These synthetic resin dispersions are recommended for coating, adhesive bonding, sealing, and impregnating.
The use of relatively expensive monoethylenically unsaturated acetophenone derivatives and/or benzophenone derivatives, and of unsaturated ketone derivatives and/or aldehyde derivatives and a compound containing at least two acid hydrazide groups which is added subsequently, means that the corresponding synthetic resin is itself relatively expensive. A disadvantage of these synthetic resins is that films thereof, despite attaining high values of elongation at break, lack sufficient resilience following a defined extension, either through application of a defined weight or following extension by a defined distance, and remain, accordingly, in the extended state. A further disadvantage of coatings comprising these synthetic resins is that they frequently prove to be of poor stability to water exposure a short time following their application to the substrate, and exhibit high water absorption. Furthermore, these coatings in many cases exhibit a strong tendency toward reemulsification and/or blistering after brief exposure to water vapor.
EP-A-0 599 676 discloses aqueous polymer dispersions whose synthetic resins include not only monomers such as acrylic or methacrylic esters and styrene but also monoethylenically unsaturated acetophenone derivatives and/or benzophenone derivatives and also have an oxygen-reactive dicyclopentadienyl group. These synthetic resin dispersions are recommended for elastic coatings.
Disadvantages of these binders are that the process of crosslinking of paint films of these binders is relatively slow to proceed, and the paint lacks adequate elasticity in the sense of resilience following cracking-induced extension of the paint. Furthermore, stark differences may arise in the properties of a coating based on such synthetic resins depending on whether it is applied to the sun-facing side of a building or to an area not exposed to the sun. Furthermore, during the preparation of the synthetic resin dispersions by means of free-radical polymerization, allylic double bonds have an inhibiting action and so hinder the preparation of these dispersions.
EP-A-0 778 296 relates to aqueous polymer dispersions whose synthetic resins contain in copolymerized form not only monomers such as acrylic or methacrylic esters but also methylstyrene or other alkyl-substituted styrenes and, optionally, acrylonitrile. These synthetic resin dispersions are recommended as binders for elastic coatings and sealing compounds.
Disadvantages of these binders are that the process of crosslinking of paint films of these binders is relatively slow to proceed under the influence of light, and the paint lacks adequate elasticity in the sense of resilience following cracking-induced extension of the paint. Furthermore, stark differences may arise in the properties of a coating based on such synthetic resins depending on whether it is applied to the sun-facing side of a building or to an area not exposed to the sun. A further disadvantage of coatings with these synthetic resins is that they are in many cases of poor stability to water exposure shortly after application to the substrate. Furthermore, these coatings in many cases exhibit a strong tendency toward reemulsification and/or toward blistering following brief exposure to water vapor. The use of acrylonitrile in these binders results, moreover, both in a readiness toward yellowing and in poor stability of the coatings with respect to basic substrates owing to hydrolysis of the acrylonitrile group in the copolymer, which leads to a greatly increased sensitivity to water.
It was an object of the present invention, therefore, to develop a synthetic resin which features, in the coating, both low water absorption and particularly low reemulsifiability following treatment with water vapor, in combination with good elongation at break and good relaxation following defined extension.
This object is achieved by an aqueous copolymer dispersion consisting essentially of
A) an aqueous dispersion of a copolymer having a solids fraction of from 20 to 65% by weight, said copolymer being composed of
a) from 40 to 99.9% by weight, preferably from 65 to 85% by weight, of at least one ester of a,p-monoethylenically unsaturated carboxylic acids containing 3 to 6 carbon atoms and alkanols containing 1 to 18 carbon atoms and from 0 to 40% by weight, preferably from 15 to 35% by weight, of at least one vinylaromatic compound (monomers a),
b) from 0.05 to 10% by weight of at least one xcex1,xcex2-monoethylenically unsaturated mono- or dibasic acid containing 3 to 8 carbon atoms, and/or anhydrides thereof, and from 0 to 10% by weight of at least one xcex1,xcex2-monoethylenically unsaturated carboxamide which contains 3 to 8 carbon atoms and can be substituted once or twice on the nitrogen by alkyl ether sulfates, alkyl sulfates, alkanols or alkyls containing up to 5 carbon atoms (monomers b),
c) from 0.05 to 10% by weight of at least one monoethylenically unsaturated crosslinking monomer (monomers c), and
d) from 0 to 30% by weight of at least one other copolymerizable monoethylenically unsaturated monomer (monomers d), in copolymerized form,
the weight fractions of the monomers a, b, c and d being chosen within the stated limits such that a synthetic resin composed of these monomers alone would have a glass transition temperature in the range from xe2x88x9250 to 35xc2x0 C., preferably from xe2x88x9240 to 10xc2x0 C. and, with particular preference, from xe2x88x9230 to xe2x88x9210xc2x0 C.,
B) from 0 to 10% by weight, preferably from 0.02 to 2% by weight, based on the copolymer A, of benzophenone, acetophenone, one or more acetophenone derivatives or benzophenone derivatives without an ethylenically unsaturated group, or a mixture thereof,
C) from 0.3 to 10% by weight, based on the copolymer A, of emulsifiers, and
D) from 0 to 5% by weight, preferably from 0.05 to 5% by weight, based on the copolymer A, of protective colloids.
The compounds used as esters of xcex1,xcex2-monoethylenically unsaturated carboxylic acids containing 3 to 6 carbon atoms and alkanols containing 1 to 18 carbon atoms are preferably the esters of acrylic and/or methacrylic acid. Of these, particular importance is attached to the esters of methanol, of ethanol, of the propanols, of the butanols, of the pentanols, of 2-ethylhexanol, of isooctanol, of n-decanol and of n-dodecanol. Preferred vinylaromatic compounds are styrene, methylstyrene, ethylstyrene, dimethylstyrene, diethylstyrene and trimethylstyrene, particular preference being given to styrene.
The compounds used as xcex1,xcex2-monoethylenically unsaturated mono- or dibasic acids containing 3 to 8 carbon atoms are preferably xcex1,xcex2-monoethylenically unsaturated carboxylic acids and their water-soluble derivatives; with particular preference, acrylic acid, methacrylic acid, ethacrylic acid, itaconic acid, fumaric acid and maleic acid, and their anhydrides. Also suitable, furthermore, are the amides and monoamides of these acids, preference among these being given to acrylamide and methacrylamide and also their N-substituted derivatives such as N,(Nxe2x80x2-di)methyl(meth)acrylamide, N,(Nxe2x80x2-di)ethyl(meth)acrylamide and N,(Nxe2x80x2-di)isopropyl(meth)acrylamide. Methacrylamide is particularly preferred. Acrylamide derivatives which are substituted once or twice on the nitrogen by alkyl, alkanol, alkyl sulfate or alkyl ether sulfate radicals containing up to 5 carbon atoms may also be present. In addition, vinylsulfonic acid, vinylphosphonic acid, acrylamidoglycolic acid and methacrylamidoglycolic acid are very suitable. These synthetic resins preferably contain in copolymerized form 0.3 to 5% by weight of the monomers b. Particular preference is given to a mixture of acrylic acid and methacrylic acid as monomers b, in particular a mixture of acrylic acid, methacrylic acid and methacrylamide.
Preferred monomers c are silanes of the formula CH2xe2x95x90CHxe2x80x94Si(OX)3 in which X is a hydrogen atom, an acyl group and/or an alkyl group having not more than three carbon atoms. Vinyltrimethoxysilane, vinyltriethoxysilane and vinyltris-2-methoxysilane are particularly preferred. Further preferred monomers c are silanes of the formula CH2xe2x95x90CZxe2x80x94COOxe2x80x94Yxe2x80x94Si(OX)3, in which Z is a hydrogen atom or a methyl and/or ethyl group, Y is a group CnH2n where n=2 to 6, and X is a hydrogen atom, an acyl group and/or an alkyl group having not more than three carbon atoms, with particular preference xcex1-methacryloxypropyltrimethoxysilane, and also glycidyl (meth)acrylates or other ethylenically unsaturated derivatives of glycidol, such as glycidyl vinyl ether, for example. It is possible, furthermore, to use monomers containing keto groups, such as acetoacetoxy-functional monomers, examples being acetoacetoxyethyl methacrylate, acetoacetoxybutyl methacrylate, acrylamidomethylacetylacetone and vinyl acetoacetate, polymerizable derivatives of diacetone, such as diacetoneacrylamide and diacetonemethacrylamide, and also acrolein. Further candidates for use as monomers c are alkoxyvinylsilanes, (meth)acryloyloxy-alkylsilanes, (meth)acryloyloxyalkyl-sulfonates, sulfates or phosphates, ethenesulfonate and polymerizable ethyleneurea derivatives, such as N-(xcex2-(meth)acryloxyethyl)-N,Nxe2x80x2-ethyleneurea and N-(xcex2-acrylamidoethyl)-N,Nxe2x80x2-ethyleneurea.
As monomers d it is preferred to use acrylic or methacrylic esters of diols, such as, for example, hydroxyalkyl (meth)acrylates, especially hydroxyethyl acrylate or 1,4-butanediol monoacrylate, and also acrylic or methacrylic esters of tetrahydrofurfuryl alcohol, halogen-containing monomers such as vinyl chloride and vinylidene chloride, unsaturated hydrocarbons such as ethylene, propylene, isobutene, butadiene and isoprene, and lower vinyl ethers. Unsaturated nitrogen compounds can likewise be used as monomers d, such as N-vinylformamide, N-vinylpyrrolidone, tetrahydrofurfurylamine, acrylonitrile and methacrylonitrile, and also the ureido monomers such as xcex2-ureidoethyl acrylate, xcex2-ureidoethyl vinyl ether, N-dimethylaminoethyl-Nxe2x80x2-vinyl-N,Nxe2x80x2-ethyleneurea and N-methylaminoethyl-Nxe2x80x2-vinyl-N,Nxe2x80x2-ethyleneurea. Also suitable are the monoesters of xcex1,xcex2-monoethylenically unsaturated dicarboxylic acids containing 4 to 8 carbon atoms and alkanols containing 5 to 20 carbon atoms.
Particular interest attaches to synthetic resins A whose monomer components a, b, c and d are selected such that a synthetic resin composed of these monomers alone would have a glass transition temperature of from xe2x88x9240 to 10xc2x0 C., in particular from xe2x88x9230 to xe2x88x9210xc2x0 C. According to Fox (T. G. Fox, Bull. Am. Phys. Soc. (Ser. II) 1, 123 [1956]) the glass transition temperature of copolymers is given in good approximation by       1    Tg    =                    X        1                    Tg        1              +                  X        2                    Tg        2              +          …      ⁢              xe2x80x83            ⁢                        X          S                          Tg          S                    
where X1, X2, . . . , XS are the mass fractions of the monomers 1,2, . . . , s and Tg1, Tg2, . . . TgS are the glass transition temperatures of the homopolymers of each of the monomers 1,2, . . . or s, in degrees Kelvin. The glass transition temperatures of the homopolymers composed of the monomers a and b, respectively, are essentially known and are listed, for example, in J. Brandrup, E. H. Immergut, Polymer Handbook, 1st Ed., J Wiley, New York, 1966, and 2nd Ed. J. Wiley, New York,1975.
Acetophenone, benzophenone and also acetophenone derivatives or benzophenone derivatives containing no ethylenically unsaturated groups have proven suitable as component B. Particular preference is given to the use of benzophenone and/or a benzophenone derivative without an ethylenically unsaturated group; mixtures of benzophenone and suitable auxiliary substances that are liquid at room temperature are particularly advantageous from a technical standpoint. Mixtures of this kind are known inter alia from EP-A-0 209 831.
The fraction of component B, based on the copolymer A, is preferably in the range from 0.05 to 5% by weight. Component B is incorporated judiciously by stirring, preferably with heating, into an initial dispersion containing at least one synthetic resin A. In this case the incorporation of component B by copolymerization is avoided, so as to achieve only surface crosslinking under atinic light in the fully formulated coating, whereas the properties of the coating are obtained by internal crosslinking with the monomers c. The incorporation of unsaturated benzophenone derivatives by copolymerization would bring about a more uniform distribution of the benzophenone functionalities but at the same time would result in a deterioration in the elastic properties following prolonged irradiation with atinic light, since subsequent internal crosslinking would take place in the film.
As emulsifiers C it is preferred to use nonionic and/or ionic emulsifiers.
Examples of nonionic emulsifiers which can be used are alkyl polyglycol ethers such as ethoxylation products of lauryl, oleyl or stearyl alcohol or of mixtures such as coconut fatty alcohol; alkylphenol polyglycol ethers such as ethoxylation products of octyl- or nonylphenol, diisopropylphenol, triisopropylphenol or of di- or of tri-tert-butylphenol; or ethoxylation products of polypropylene oxide.
Suitable ionic emulsifiers are preferably anionic emulsifiers. These can be the alkali metal salts or ammonium salts of alkyl-, aryl- or alkylaryl-sulfonates, alkyl, aryl or alkylaryl sulfates or phosphates, or alkyl-, aryl- or alkylaryl-phosphonates or compounds with other anionic end groups, it also being possible for oligoethylene oxide or polyethylene oxide units to be present between the hydrocarbon radical and the anionic group. Typical examples are sodium lauryl sulfate, sodium undecyl glycol ether sulfate, sodium lauryl diglycol sulfate, sodium tetradecyl triglycol sulfate, sodium octylphenol glycol ether sulfate, sodium dodecylbenzenesulfonate, sodium lauryl diglycol sulfate, and ammonium tri-tert-butylphenol penta- or octaglycol sulfate.
Compounds used as protective colloids D are preferably water-soluble carboxymethylcelluloses having a degree of substitution of from 0.4 to 2.9, preferably 0.4 to 1.5 and, with particular preference from 0.6 to 1.4, the degree of substitution denoting the average number of carboxymethyl groups introduced per anhydroglucose unit, whose 2% strength aqueous solutions have a Brookfield viscosity (20 rpm) at 25xc2x0 C. of less than 2000 (with spindle 3), preferably below 500 (with spindle 2) and, with particular preference, below 100 (with spindle 1) mpas. The carboxymethylcellulose is preferably used in the form of its ammonium or alkali metal salt. Examples of suitable commercial products are Blanose 7M(copyright), Blanose 7UL(copyright) and Blanose 7EL(copyright) from Clariant GmbH, and also Ambergum 3021(copyright) from Aqualon. The carboxymethylcelluloses of the invention can if desired include further substituents as well, especially alkyl or hydroxyalkyl radicals having 1 to 4 carbon atoms, alkyloxyalkyl radicals having 2 to 6 carbon atoms or dialkylamino radicals having a total of 2 to 6 carbon atoms. Examples of particularly suitable compounds are methylcarboxymethylcellulose, ethylcarboxymethylcellulose, hydroxyethylcarboxymethylcellulose, hydroxypropylcarboxymethylcellulose, methoxyethylcarboxymethylcellulose, ethoxyethylcarboxymethylcellulose and diethylaminocarboxymethylcellulose. Examples of further protective colloids which can be used are high molecular mass compounds such as polyvinyl alcohols, polyvinylpyrrolidones, polyacrylamides, polymethacrylamides, polycarboxylic acids or their alkali metal and/or ammonium salts.
The polymers to be used as synthetic resins A can be prepared by the known methods of free-radical bulk, solution, suspension and emulsion polymerization. The preferred mode of preparation of the aqueous synthetic resin formulation of the invention is, however, the aqueous form, and it is therefore advisable to use the synthetic resin A in this form as well. Accordingly, said resin is prepared preferably by polymerizing the respective monomers in an aqueous medium under the known conditions of free-radical emulsion polymerization in the presence of water-soluble free-radical initiators and emulsifiers C and also, if desired, in the presence of protective colloids D, regulators and/or further auxiliaries. The polymerization is conducted in accordance with the customary techniques of emulsion polymerization, by emulsifying the monomers in the aqueous phase in the presence of emulsifiers, initiators and the protective colloid and polymerizing them at temperatures from 60 to 95xc2x0 C. The emulsion polymerization can be conducted in accordance with the customary techniques known to the skilled worker, such as batch, monomer metering or emulsion feed techniques. It is preferred to operate in accordance with the emulsion feed technique, in which a small amount of the monomers is subjected to initial polymerization and then the remaining amount of monomers is metered in as an aqueous emulsion. If desired, it is also possible for a plurality of different monomer emulsions to be metered in one after another. Like the emulsifier, the protective colloid can be included partly in the initial charge to the reactor and/or metered in with the monomer emulsion.
The preparation of high-quality dispersions in accordance with the present invention presupposes the application of the knowledge which exists in the field of emulsion polymerization, even where that knowledge is not described here. Failure to observe the rules known to the skilled worker in the art of emulsion polymerization can therefore adversely affect important properties, an example being the water resistance of the dispersion films. Based on the amount of polymer, therefore, the dispersions should not substantially exceed the amounts preferably used of up to 3% by weight, with particular preference up to 2% by weight, of ionic emulsifiers and/or of up to 6% by weight, with particular preference up to 4% by weight, of nonionic emulsifiers. In particular, use is made only of ionic emulsifiers in an amount of xe2x89xa62% by weight.
In order to initiate and carry out the polymerization use is made of oil-soluble and/or, preferably, water-soluble free-radical initiators or redox systems. Suitable examples are hydrogen peroxide, potassium, sodium or ammonium peroxodisulfates, dibenzoyl peroxide, lauryl peroxide, tri-tert-butyl peroxide, bisazodiisobutyronitrile, alone or together with reducing components, e.g., sodium bisulfite, Rongalit(copyright), glucose, ascorbic acid, and other compounds having a reducing action. Particular preference is given to the use of peroxodisulfates.
In the emulsion polymerization the temperature is generally from 30 to 90xc2x0 C., preferably from 50 to 90xc2x0 C., and the polymerization initiators are used typically in amounts of from 0.1 to 10% by weight, based on the total amount of monomers.
It is further possible to use regulators, such as mercaptans, especially n-dodecyl mercaptan, thiophenol, and 2-methyl-5-tert-butylthiophenol. Amounts of from 0 to 1 by weight, preferably from 0 to 0.5% by weight, are typically used, and with particular preference the dispersion is prepared using xe2x89xa60.3% by weight of a regulator.
The dispersions are typically adjusted to a pH of from 6.5 to 10, preferably from 7.0 to 9.0, using aqueous ammonia solutions, alkali metal hydroxide solutions and alkaline earth metal hydroxide solutions.
If desired, the dispersion may further comprise film forming auxiliaries, such as white spirit, Texanol(copyright), butyldiglycol and butyldipropylene glycol, plasticizers, such as dimethyl phthalate and dibutyl phthalate, dispersants such as polyacrylic acids and corresponding copolymers such as, for example, Lopon 890(copyright) and Dispex G40(copyright), thickeners based on polyacrylates or polyurethanes such as, for example, Borchigel L75(copyright) and Tafigel PUR 40(copyright), preservatives, defoamers such as, for example, mineral oil or silicone defoamers, wetting agents, such as aminomethylpropanol, and other additives typical in formulating coating compositions.
The synthetic resin formulations of the invention are particularly suitable for use in coating compositions for walls, floors and ceilings, as elastic binders for leather fibers, and as marking paints for paths and highways, and also in renders, where they ensure durable bridging of cracks, low tack and low soiling tendency, and good resistance to water.
The present invention is described in more detail below with reference to working examples but without being restricted thereby.
A monomer mixture of 50 g of n-butyl acrylate, 20 g of ethylhexyl acrylate, 27 g of styrene, 2 g of methacrylic acid and 1 g of vinyltrimethoxysilane with 1.8 g of the Na salt of C12-alkyl triglycol ether sulfate is emulsified in 100 g of water.
Subsequently, 10% of an aqueous solution of 0.5 g of sodium peroxodisulfate in 10 g of water is added to 10% of the aqueous emulsion and this mixture is heated with stirring to a temperature of 80xc2x0 C. Subsequently, over the course of 2 hours, the remaining amount of the aqueous emulsion and, in parallel but over the course of 2.5 hours, the remaining amount of the aqueous initiator solution are supplied continuously with stirring. The polymerization temperature is 80xc2x0 C.
Following the end of metered addition of the initiator, polymerization is continued for a further hour.
0.7 g of benzophenone is stirred into the resulting, approximately 50%, aqueous synthetic resin dispersion.
A monomer mixture of 50 g of n-butyl acrylate, 20 g of 2-ethylhexyl acrylate, 27 g of styrene and 2 g of methacrylic acid, without vinyltrimethoxysilane, with 1.8 g of the Na salt of C12-alkyl triglycol ether sulfate is emulsified in 100 g of water.
Subsequently, 10% of an aqueous solution of 0.5 g of sodium peroxodisulfate in 10 g of water is added to 10% of the aqueous emulsion and this mixture is heated with stirring to a temperature of 80xc2x0 C.
Subsequently, over the course of 2 hours, the remaining amount of the aqueous emulsion and, in parallel but over the course of 2.5 hours, the remaining amount of the aqueous initiator solution are supplied continuously with stirring. The polymerization temperature is 80xc2x0 C. Following the end of metered addition of the initiator, polymerization is continued for a further hour.
0.7 g of benzophenone is stirred into the resulting, approximately 50%, aqueous synthetic resin dispersion.